Densitometer for absolute measurements of the temperature dependence of density, partial volumes, and thermal expansivity of solids and liquids

A densitometer device is described which can be used for rapid absolute determination of the temperature dependence of density, partial volumes, and thermal expansivity of condensed matter. The instrument is based on the hydrostatic method. It employs a two-chamber measuring system and an electronic balance. It can be used at both low (down to −100 °C) and high (up to 300 °C) temperatures. A small, polished buoyancy body of fused silica serves as a calibration standard. The theoretical foundations of hydrostatic density measurements are reviewed and pilot experiments are reported. Samples investigated are, e.g., silicon, LD polyethylene, n-hexane, methanol, and toluene. The information obtained refers among others to the stirrup buoyancy, the time course of thermodynamic equilibration after change of temperature, the temperature dependence of density and specific volume of methanol, etc. The results demonstrate that the instrument can be used for precise, rapid densitometric investigations of small samples of solids (5–700 mg) and liquids (5–100 cm3), independent of form and shape, at both low and high temperatures. The measurements can also be carried out dynamically by use of scanning techniques so that thermally deduced density changes can be observed directly in continuous fashion. For a self-consistent relative density determination relative to the calibration standard itself, the onset of inaccuracy is in the fifth decimal (<±0.01%), whereas for direct absolute measurements it is, at present, in the fourth decimal (<±0.1%).